Coal liquefaction process

ABSTRACT

A process for producing liquid hydrocarbonaceous products from coal utilizing two steps of solvent extraction with different solvents. In the first stage, coal is contacted, at relatively high temperature and pressure, with a heavy hydrocarbon solvent containing a mixture of hydroaromatic hydrocarbons and saturated aliphatic hydrocarbons in a hydroaromatics/aliphatics weight ratio between about 1:2 and about 2:1. The solid materials remaining after the first liquefaction step are subsequently separated from the liquefied coal and the heavy solvent and the liquefied coal from the first extraction step is recovered as a product. The solid materials recovered from the first extraction step are solvent extracted, at relatively low temperature and pressure, with a monocyclic aromatic hydrocarbon solvent, and the resulting liquids are also recovered as a product.

United States Patent Gleim et al.

[ COAL LIQUEFACTION PROCESS [75] Inventors: William K. T. Gleim, IslandLake;

Mark J. OHara, Mt. Prospect, both of I11.

[73] Assignee: Universal Oil Products Company, Des Plaines, Ill.

[22] Filed: Apr. 9, 1973 [21] Appl. No.: 349,344

[52] US. Cl. 208/8 51] Int. Cl .[Cidg 1704" 58 Field of Search, .2 208/81 [56] References Cited "UNITED STATES PATENTS 3,583,900 6/1971Gatsis 208/8 3,607,716 9/1971 Roach.... 208/8 3,607,717 9/1971 Roach208/8 3,607,718 9/1971 Leadersetal. 2 s[ s i Primary Examiner-VeronicaOKeefe m V I itfbfieyfAgeFr] bTFTfriz fanie s' RITloatson, J"'r.;'Thomas K McBride; William H. Page, ll

57] ABSTRACT A process for producing liquid hydrocarbonaceous productsfrom coal utilizing two steps of solvent extraction with differentsolvents. ln the first stage, coal is contacted, at relatively hightemperature and pressure, with a heavy hydrocarbon solvent containing amixture of hydroaromatic hydrocarbons and saturated aliphatichydrocarbons in a hydroaromatics/aliphatics weight ratio between about1:2 and about 2:1. The solid materials remaining after the firstliquefaction step are subsequently separated from the liquefied coal andthe heavy solvent and the liquefied coal from the first extraction stepis recovered as a product. The solid materials recovered from the firstextraction step are solvent extracted, at relatively low temperature andpressure, with a monocyclic aromatic hydrocarbon solvent, and theresulting liquids are also recovered as a product.

6 Claims, N0 Drawings 1 COAL LIQUEFACTION PROCESS BACKGROUND OF THEINVENTION This invention concerns a process for converting solidcarbonaceous materials such as coal into liquid hydrocarbonaceousproducts. More particularly, this invention relates to a process forsolvent extracting coal, using two different solvents in two extractionsteps, to provide hydrocarbonaceous liquid suitable for use assubstitutes for petroleum liquid.

Solvent extraction of coal and similar carbonaceous materials is knownas a method for producing hydrocarbonaceous liquids. The liquid productfrom such extraction operations may be substituted for petroleumfractions and can be refined to produce gasoline, etc., in a manneranalogous to that used to refine petroleum liquids. Because of theabundance of coal reserves and decreasing petroleum resources, it ispresently becoming increasingly important to develop practical methodsfor deriving petroleum substitutes from coal.

In a typical operation for solvent extraction of coal, the coal ispulverized and mixed with a hydrocarbonaceous solvent. The mixture ofcoal and solvent, typically with hydrogen gas included, is subjected tohead and pressure. A fraction of the coal is dissolved and mixed withthe solvent. The liquid mixture of solvent and dissolved coal is thenseparated from the coal ash and undissolved coal by settling,filtration, etc. Two problems in particular have created substantialdifficulties in attempts to develop economical methods for solventextracting coal. These difficulties can be characterized briefly as,first, inability to facilitate the transfer of sufficient hydrogen intothe hydrogen-deficient coal during the extraction step and, second, lackof selectivity of the solvent used in extracting particular componentsof the coal. Since the coal to be extracted is relatively low inhydrogen content, it is necessary to add a significant amount ofhydrogen to the coal during a solvent extraction operation. In order toform coal liquids which can be used as substitutes for petroleumfractions, the hydrogen content of the coal to be liquetied must beincreased typically from about 5 weight percent of the coalup to aboutweight percent or more of the liquefied materials. Prior art has devisedseveral methods for facilitating the necessary hydrogen addition. Ofthese, the most commonly suggested has been the use of extraneouscatalysts and the use of hydrogen donor solvents.

The use of'extraneous catalysts has been found generally impractical.These catalysts rapidly become poisoned by the metals naturally presentin the coal, and are quite difficult to separate from the solid residueremaining after the extraction operation. Hydrogen donor solvents haveprovided a partial solution to the problem of transferring hydrogen intothe coal. These solvents donate hydrogen to the coal molecules andsimultaneously revert from a partially saturated to an aromaticstructure. However, the amount of hydrogen which such hydrogen donorsolvents can normally transfer into the coal is quite limited, and afurther hydrogenation treatment of the coal extract subsequent to anextraction operation is generally necessary when using hydrogen donorsolvent to extract coal.

Lack of selectivity of coal solvents in extracting the various availablecomponents of coal is a problem related to the inability of solvents totransfer sufficient hydrogen into the coal as discussed above. Lack ofselectivity is found generally in prior art solvents, but will bediscussed hereinafter in terms of hydrogen donor solvents, since theyhave generally been employed to the exclusion of other solvents.Hydrogen donor solvents are capable of dissolving a large fraction ofthe solid coal, often as much as percent. Unfortunately, the coalliquids obtained by using hydrogen donor solvents invariably contain asmuch as 40 50 percent of undesirable components which are substantiallyrefractory to further refining, are severely hydrogen sufficient andseverly inhibit separation and refining of the more valuable componentsof the coal. For convenience, these undesirable components of coalextracts can be characterized as benzene-insoluble components andbenzene-soluble but heptane-insoluble components. The benzene-insolublecomponents of coal liquids are generally thought to result primarilyfrom polymerization of dissolved components of the coal subsequent totheir extraction into the solvent. During the extraction operation, themolecules in the original solid coal are depolymerized and partiallyhydrogenated. Because of the lack of available hydrogen, a significantfraction of the liquefied materials remains in an easily polymerizablestate and tends to repolymerize rapidly to form undesirable, highmolecular weight compounds which are even more refractory than theoriginal solid coal. Since prior art solvents, including the hydrogendonor type, are unable to supply sufficient hydrogen to saturate orcrach these polymerizable compounds, they rapidly revert to undesirable,benzene-insoluble refractory compounds in prior art extractionoperations. It is thus apparent that simply dissolving a large fractionof the original solid coal, without adequate hydrogenation, is not onlyfutile, but actually undesirable. The polymerizable compounds which areproduced by such operations cannot be adequately hydrogenated usingprior art solvents and will rapidly form undesirable and untreatablebenzeneinsoluble compounds. It has been found that a separate supply ofhydrogen gas mixed with prior art solvents and coal is not sufficient toprovide an adequate source of hydrogen which can be effectively utilizedin the extraction operation, since uptake of the hydrogen gas into thesolvent and transfer therefrom into the coal molecules is not rapidenough.

The benzene-soluble but heptane-insoluble fraction found in coal liquidsis herein termed the asphaltenes" fraction. Generally, a hydrogen donorsolvent dissolves a significantly large amount of asphaltenes, e.g.,about 10 percent or more of the dissolved coal. Asphaltenes are highmolecular weight, hydrogen-deficient compounds which are difficult totreat by conventional refining techniques. A particular drawback ofasphaltenes is that they are undistillable and heat sensitive, and tendto form coke when exposed to distillation temperatures. This property ofasphaltenes makes it extremely difficult to distill the coal liquidsrecovered in prior art extraction operations. Asphaltenes are difficultto treat by refining methods and extremely difficult to separate frommore valuable components of the coal extract. They are, therefore, anundesirable fraction when found in comixture with distillable componentsof the coal, and reduction in the amount of asphaltenes contained in theliquids recovered by extraction of the coal or segregation of theasphaltenes components from the distillable fractions of the extract aredesirable in coal liquefaction.

Because of the refractory and/or heat sensitive nature of a substantialfraction of coal extract produced in prior art operations, and becauseof the presence of readily polymerizable compounds in coal liquids afterthe extraction step, it has been found impractical to attempt to performconventional refining operations, e.g., distillation and catalyticcracking, on coal liquids as they are recovered from extractionoperations. A further hydrogen treatment of the coal liquids aftersolvent extraction has been found necessary in prior art in order tomake the coal liquids suitable for catalytic cracking and distillation.The type of hydrogen utilized with these extracts is cumbersome andentails the use of expensive catalysts and high temperatures. Theexpense and difficulties of such post-extraction hydrogenationoperations, when performed on the extract as a whole, has beensignificant barrier to the development of a successful process forsolvent extracting coal to provide petroleum substitutes. As describedabove, the use of extraneous catalysts during the solvent extractionstep itself, although successful in producing distillable coal extracts,is technically difficult and also prohibitively expensive, since suchcatalysts deactivate rapidly, requiring extensive regenerationfacilities, and are also quite difficult to separate from solid coalresidues. l

A drawback generally found in prior art liquefaction solvents andprocesses is the effect of the extraction operations on coal subjectedto extraction which is not dissolved during the operation. Any of thecoal which is not dissolved in a first extraction operation on theoriginal coal has been found quite refractory in any further subsequentextraction. This is partly the result of the failure, discussed above,of prior art solvents to transfer sufficient quantities of hydrogen intothe coal during the extraction step. Any of the coal not dissolved isthus quite hydrogen-deficient, and has, if anything, less hydrogencontent than the original coal. Coal is thus degraded by prior artextraction operations into a relatively undesirable form, and is notfurther extractable in a practical manner. Since the object of solventextraction operations is to convert coal into petroleum substitutes, itis obviously desirable to treat the coal by an extraction operation in amanner which converts the unliquefied, solid coal to a form moresusceptible to conversion to a liquid rather than to degrade theunliquefied coal into a low value source. Such degradation of theunconverted coal has been a barrier to successful solvent extractionoperations when selective conversion of only a fraction of the originalcoal has been attempted using, for example, hydrogen donor solvents.

SUMMARY OF THE INVENTION An object of the present invention is toprovide a process for the liquefaction of coal and similar carbonaceoussolids to form hydrocarbonaceous 'liquids which can replace petroleumfractions and products.

Another object of the present invention is to provide a coalliquefaction process in which components of solid coal are selectivelyextracted in an operation using two stages of extraction of solid coal.

Another object of the present invention is to provide a process forsolvent extraction of coal using two extraction steps which provides ahydrocarbonaceous liquid product substantially free from non-distillablecomponents.

Another object of the present invention is to provide a process for theextraction of coal in which the transfer of hydrogen into the coalduring the liquefaciton of the coal is enhanced.

Another object of the present invention is to provide a coalliquefaction process which produces a liquefaction product which can besubjected directly to conventional catalytic cracking withoutintermediate hydrogenation treatment.

Another object of the present invention is to provide a process forliquefying coal which produces a liquefaction product substantially freefrom polymerizable, high molecular weight components.

Another object of the present invention is to provide a process forliquefying coal using two steps for extracting the coal solids, in whichthe first extraction step enhances the hydrogen content and solubilityof the coal not liquefied during the first extraction step.

In an embodiment, the present invention relates to a process forproducing liquid hydrocarbonaceous products from a solid carbonaceousmaterial which comprises the steps of contacting the solid carbonaceousmaterial, at liquefaction conditions, with a liquefaction solventcomprising a combination of a hydroaromatic hydrocarbon component and asaturated aliphatic hydrocarbon component with a hydroaromatic component/saturated aliphatic component weight ratio of about 1:2 to about2: l; separating the resulting mixture into a solid phase and a liquidphase; recovering a first hydrocarbonaceous product from the liquidphase; contacting the solid phase with a monocyclic aromatic hydrocarbonat solvent extractant conditions; and, recovering a secondhydrocarbonaceous product from the resulting mixture.

We have found that when a coal liquefaction solvent containing a mixtureof hydroaromatic hydrocarbons and saturated aliphatic hydrocarbons, at aweight ratio of about 1: 2 to about 2:1, is employed in a firstliquefaction step, the coal liquids recovered are substantially freefrom polymerizable and coke forming components. Even more important, thecoal solids which are not liquefied during the first extraction step aremodified in-a very' beneficial manner. The unliquefied portion of thecoal treated in a first liquefaction step using the aforesaid solventmixture is rendered soluble in a monocyclic aromatic solvent such asbenzene at extraordinarily mild extraction conditions which are utilizedin a second extraction step in the present process.

DETAILED DESCRIPTION OF THE INVENTION The solid carbonaceous materialswhich may be solvent extracted utilizing the process of the presentinvention includes in general, coal, lignite, peat, oil shale, tar sand,and like naturally occurring carbonaceous materials. The presentinvention is particularly applicable to the conversion of bituminouscoal. A typical preferred bituminous coal is an Illinois bituminousstoker coal having a volatile content of about 5 percent or higher inthe moisture and ash free (MAF) coal. Although the following descriptionis given with reference only to the preferred bituminous coal, thediscussion is equally applicable to the other solid carbonaceousmaterials noted above, unless otherwise stated. In general, betterresults are obtained in the presentprocess when the coal to be extractedis pulverized to fairly small size particles, e.g., mesh particle sizeor smaller. Howsaturated aliphatic hydrocarbon components. It isessential to the present process that the first stage liquefactionsolvent contain compounds from both of these two groups. Otherhydrocarbons or extraneous materials may or may not be present invarying amounts up to about weight percent of the total liquefactionsolvent without any particular adverse effect on the results obtained inthe first liquefaction step. Preferably, compounds not fitting intoeither of the two categories of essential components in the first stageliquefaction solvent are not present in the liquefaction solvent at morethat about 10 weight percent of the solvent as a whole. The weight ratioof the two essential types of components in the first stage liquefactionsolvent is an important aspect of effective operation in both the firstand second stages of extraction in the present process. The best resultin the first stage can only be obtained by maintaining the weight ratioof the liquefaction solvent within a specified range. This weight ratioalso has a strong effect on the ability of the second stage extractionsolvent to convert a large fraction of the coal at mild conditions. Goodresults are obtained when the weight ratio of hydroaromatic compounds tosaturated aliphatic compound is maintained between about 1:2 and about2:1. A preferred weight ratio range of hydroaromatic to satuatedaliphatic components is from about 2:3 to about 3:2. The hydroaromaticcomponent of the liquefaction solvent employed in the first stageliquefaction step may be selected from a broad range of compounds whichare characterized as partially hydrogenated condensed aromatic ringswith from 1 to 4 (adjacent) CH groups in which the carbon atom of the CHgroup forms part of the condensed ring structure. An example of ahydroaromatic compound having nonadjacent CH groups is 9,1O-dihydroanthracene. An example of a hydroaromatic having two adjacentCH groups is 9,10-dihydrophenanthrene. An example of a hydroaromatichaving 3 adjacent CH groups is indane. An example of a hydroaromatichaving 4 adjacent CH groups tetrahydronaphthalene. The hydroaromaticssuitable for use in the present process have normal boiling points aboveabout 400F. and preferably above about 500F. It is generally preferredthat the hydroaromatic fraction of the solvent utilized in the firststage liquefaction step in the present invention is a mixture ofdifferent partially hydrogenated polycyclic aromatic compounds, sincepure hydroaromatic compounds, although giving equivalent results, are nomore suitable than a mixture and are expensive and difficult to obtain.While the partially saturated naphthalenic hydrocarbons, i.e.,dihydronaphthalene and tetrahydronaphthalene, are operative ashydroaromatic hydrocarbon compounds in the first stage liquefactionsolvent, the preferred hydroaromatic compounds are higher boiling,partially saturated condensed ring aromatics with structures containingthree or more condensed benzene nuclei. Examples of suitable compoundsinclude anthracene, and phenanthrene derivatives, etc. Other suitablecompounds, by way of example, include the partially saturated derivativeof naphthacene, benzoanthracene, chrysene, benzophenanthrene,triphenolene, pyrene, pentacene, benzonaphthacene, pentaphene,benzochrysene, debenzophenanthrene, dibenzoanthracene, picene,naphthanthracene, benzopyrene, perylene, hexaphene, benzopentacene,hexacene, debenzonaphthacene, debenzochrysene, benzopentacene,anthroanthracene, tribenzoanthrancene, naphthochrysene, benzopicene,phenanthrophenanthrene, naphthonaphthacene, benzoperylenes,dibenzopyrenes, heptacene, benzohexacenes, debenzopentacenes,benzohexaphene, heptaphene, anthranaphthacene, naphthopentacene,benzonaphthochrysenes, debenzopicene, debenzopentaphene, trinaphtholene,trinaphtholene, tetrabenzeanthracene, benzonaphthonaphthacene,dibenzopyrolene, naphthopyrolene, debenzopicene, naphthopicene,benzonaphthochrysene, coronene, etc. Particularly preferredhydroaromatic compounds include dihydrophenanthrene, dihydroanthracene,tetrahydroanthracene, dihydropyrene, tetrahydropyrene, and hexahydrocoronene, partially saturated condensed ring compounds having one ormore relatively short alkyl groups (e.g., 1-5 carbon atoms) in place ofone or more of the hydrogen atoms in the condensed ring structure aswell as phenyl group substituents are also suitable. It will be apparentto those skilled in the art that any mixture of partially hydrogenatedpolycyclic compounds which is derived from petroleum or coal liquids by,for example, partial hydrogenation of a particular fraction of thepetroleum or coal oil, will generally contain at least a small fractionof many or most of the above listed compounds, their alkyl substitutedor phenyl group substituted analogs, etc., in various states of partialsaturation. As noted above, the compounds which are included in the termhydroaromatic hydrocarbon as used herein are those in which thecondensed range structure is at least partially aromatically unsaturatedand at least partially saturated, with the saturated carbon atoms beingbonded to hydrogen atoms. If this condition is satisfied, the presenceor absence of short chain alkyl group substituents, phenyl groupsubstituent, etc., is not of critical importance. These short alkylchains and phenyl groups which replace some hydrogen atoms bonded to thesaturated carbon atoms in at least some of the condensed ring compoundsare not believed to play any part in the first stage liquefactionsolvent used in the present process.

The saturated aliphatic components of the liquefaction solvent utilizedin the first stage liquefaction step includes all types of alkanes andcycloalkanes having boiling points above about 400F. and preferablyabove about 500F. Thus, aliphatic saturates contained in a petroleumfraction which boils above about 400F. (which can be characterizedbroadly as the kerosene fraction and heavier) may suitably be used toprovide saturated aliphatic components for the first stage liquefactionsolvents. A mixture of paraffinic and naphthenic saturates such as istypically found in commerical sources of petroleum fractions, tar sandfractions, etc., is preferred over any particular saturated com pound,because best results are obtained using a mixture of paraffinichydrocarbons and naphthenic hydrocarbons. Examples of suitable saturatedaliphatic compounds which may be used, preferably in admixture, includeC and heavier normal paraffins and isoparaffins with at least C orhigher molecular weight preferred, C and longer chain phenyl substitutedalkanes, alkyl naphthenes, fused ring naphthenic structures, etc.

A convenient and suitable liquefaction solvent for use in the firstliquefaction stage of the present process may be derived from thebottoms product remaining after vacuum distillation of crude petroleum.Essential to achievement of good results by the use of a particularpetroleum bottoms fraction is the requirement that the particularbottoms fraction must contain condensed ring aromatic compounds andaliphatic compounds at an aromatic/ aliphatic weight ratio of about l:2to about 2:1, and preferably about 2:3 to about 3:2. The vacuum bottomsrecovered from petroleum distillation are not, per se, usable as asolvent in the first stage liquefaction step in the present process andmust be treated to increase the hydrogen content to an adequate levelbefore adequate results can be obtained in either the first stageliquefaction step or the second stage extraction step. Various suitablemethods for hydrogen treating a vacuum bottoms petroleum fraction areknown to those skilled in the art. By way of example, one method whichis suitable for hydrogenation of such a petroleum or tar sand faction,and which is a preferred method for deriving the first stage solventused in the present process, includes passing a vacuum bottoms fractionover a fixed bed of a suitable catalyst at a temperature of about 700 toabout 800F. and a hydrogen pressure of about 170 atmospheres or more. Asuitable catalyst may, for example, be a combination of a Group VI and aGroup VIII metal on a refractory inorganic support. One preferredcatalyst for such a hydrogenation operation comprises a combination ofnickel and molybdenum on an aluminasilica spherical support. Using sucha catalyst, a suitable liquid hourly space velocity (total volume ofcharge per hour divided by the volume of catalysts) of about 0.5 toabout 1 is generally maintained. Hydrogen is typically recycled in suchan operation at a rate of about 5,000 to about 15,000 cubic feet perbarrel of hydrocarbon charged. After the vacuum bottoms have beenprocessed in this or any other suitable manner in order to providesufficient fraction of the hydroaromatic compounds and saturatedaliphatic compounds essential to the liquefaction solvent used in thefirst stage liquefaction step, the light end (materials boiling belowabout 400F. and preferably all materials boiling below about 500F.) areremoved by distillation. The bottoms product remaining after removal ofthese light ends is a preferred solvent for use in the firstliquefaction step in the present process. It is essential to the use ofany petroleum fraction as a liquefaction solvent in the first, hightemperature extraction step in the present process that such a fractioncontain both hydroaroniatic compounds and saturated aliphatic compoundsin particular relative amounts. Unless aparticular hydrocarbon fractioncontains both types of compounds in sufficient quantity, it isunsuitable. For example, catalytic cracker slurry oils have beenproposed as coal solvents but, unlike the suitable hydrogenatedpetroleum and tar sand vacuum bottoms, slurry oils are unsuitable foruse as the first stage liquefaction solvent in the present process evenwhen subjected to hydrogen treatment by the method described above. Thisis believed to be the result of the composition of slurry oil, which isoverly high in aromatics content and deficient in aliphatics content.Thus, unless a mixture of pure hydro-aromatic compounds and saturatedaliphatic compounds is especially prepared for use as the first stageliquefaction solvent, particularly hydrocarbon fractions sought to beemployed as a solvent in the present process, must be analyzed todetermine their composition and if the composition is either too high inaromatics content or in aliphatics content, these solvents are notsuitable for use in the first stage of the present process. Thoseskilled in the art will recognize that the relative amount of aromaticsand aliphatics in particular, petroleum and tar sand fractions, variesover a wide range depending on the source of the petroleum or tar sand,so that not all properly hydrogenated vacuum bottoms fractions arenecessarily suitable. By analysis of particular petroleums, tar sands,or other available sources of a heavy hydrocarbon fraction, and from thedescription provided herein, it will be apparent to those skilled in theart which hydrocarbon fractions may suitably be employed in the firststage of the present process.

Liquefaction conditions utilized in the first stage extraction step inthe present process include a temperatur of 513613 600 1 to about 850 F.and a pressure of about atmospheres to about 350 atmospheres or more. Atemperature of about 675F. to about 800F. and a pressure of aboutatmospheres to about 250 atmospheres are preferred. The first stageliquefaction solvent and coal are admixed and charged to a liquefactionzone at solvent/ coal weight ration of about 1:2 to about 10:1. Asolvent/coal weight ratio of about 1:1 to about 3:1 is preferred. Thefirst extraction step of the present process may be embodied in either abatch type operation or a continuous type operation with good results.In a batch type operation, a quantity of the liquefaction solvent andcoal are admixed and placed in a suitable liquefaction reactor, such asan autoclave, subjected therin to liquefaction conditions, and thenwithdrawn after a suitable residence time. A residence time of about /2hour to about 24 hours may be employed with good results in such batchtype embodiments, with a residence time of about 2 hours to about 6hours being particularly preferred. In a continuous type operation, theliquefaction solvent and coal are continuously admixed, charged to asuitable liquefaction reactor, maintained therein at liquefactionconditions for a suitable time, and continuously withdrawn. A suitableliquid hourly spaced velocity (volume of reactants, solvent and hydrogencharged per hour divided by the volume of the reactor employed) of about0.25 to about 4 may be employed. A liquid hourly space velocity of about0.5 to about 1 is prefered. Any batch type or continuous type reactorsemployed in prior art coal liquefaction are suitable for use in thefirst stage liquefaction step in the present process.

After the first stage liquefaction operation, the resulting mixture ofthe liquefaction solvent, liquefied coal, solid coal, ash and lightgases is withdrawn from the liquefaction reactor and the liquefied coalis recovered as a product of the process. The coal liquids and solventare separated from the solid materials at this point by settling,filtration, centrifugation, hydroclone, extraction with light solvents,or othersimilar methods well known in the prior art. Any suitable methodfor separating the ash and other solids from the liquid materials may beutilized in the present process. After separation of the solidmaterials, the first stage coal liquid and solvent may be fractionateddirectly without any further treatment (by hydrogenation) as has beenfound necessary in prior art non-catalytic coal liquefaction operations.A fraction of the liquids recovered from the first stage liquefactionzone may by recycled, in a continuous type operation, for use as a partof the first stage liquefaction solvent or in some cases the wholesolvent in such a fraction conforms to the composition of the firststage liquefaction solvent described above as necessary to adequateoperation of the present process. The fraction of the original solidcoal which is converted to liquid hydrocarbonaceous products in thefirst stage liquefaction step of the present process is generallymaintained between about 20 weight percent and about 70 weight percentof the original coal. Preferably, the amount of liquefaction in thefirst liquefaction step is between about 45 weight percent and about 60weight percent of the original coal.

The aromatic hydrocarbons which may be employed as the extractionsolvent in the second extraction step in the present process includebenzene and alkylbenzenes. Suitable alkylbenzenes include, for example,toluene, ethylbenzene, isopropylbenzene, butylbenzenes, xylenes,diethylbenzenes, methylethylbezenes, polymethylbenzenes,polyethylbenzenes, etc. The lower boiling alkyl benzenes, such astoluene, xylenes, ethylbenzenes, cumene, etc., are preferred, andbenzene is especially preferred.

Solvent extraction conditions employed in the second stage extractionstep in conjunction with the monocyclic aromatic solvent include atemperature in the range from about 50F. to about 300F. and a pressuresufficient to maintain the solvent employed at least partially in theliquid phase. Generally, adequate pressures range from about 1atmosphere to about atmospheres or more. Extraction can be accomplishedin the second stage more rapidly at higher temperatures and pressures,but lower temperatures and pressures, e.g., about 75F. to about 200F.,and atmospheric pressure to about 5 atmospheres, are generally preferredbecause they are more economical. The second extraction step can beperformed in either a batch type operation or a continuous typeoperation. In a batch type operation a quantity of the solid residueremaining after the first liquefaction step and a quantity of monocyclicaromatic solvent are placed in a suitable batch extraction zone, suchas, for example, a Soxhlet extractor, and contacted at solventextraction conditions therein for about V2 hour to about 24 hours. Whenbenzene is employed as the extraction solvent, 21 contact time of about1 hour to about 6 hours is generally preferred. In a continuous typeoperation, solid residue from the first stage liquefaction step and themonocyclic aromatic solvent are continuously admixed an charged to asuitable continuous reactor and contacted therein at appropriateconditions of temperature and pressure for a resident time of about 0.5to about 25 hours. The monocyclic aromatic solvent and the undissolvedmaterials recovered from the first liquefaction operation may becontacted in either cocurrent or countercurrent fashion in continuoustype operation in the second extraction stage.

After an appropriate contact time between the monocyclic aromatichydrocarbon solvent and the coal solids in the second stage extractionstep, remaining solid residue is separated from the monocyclic aromaticsolvent and coal liquids dissolved therein by any suitable conventionalmeans. The aromatic solvent and liquefied coal may be separated from ashand any other insoluble solids by filtration, centrifugation, etc. Ithas been found that about 20 weight percent to about 40 weight percentof the coal undissolved after the first stage extraction is dissolvedwhen the coal is subjected to the second stage extraction step in thepresent pro cess, so that the solids remaining after the secondextraction operation are composed primarily of fusain and inorganic ash.Solid residue from the second extraction step is therfore discarded. Thecoal liquids recovered in the second extraction step are similar to theliquids recovered by prior art coal liquefaction methods. That is, thesecond stage extraction product is not directly distillable (in contrastto the coal liquids recovered in the first stage liquefaction step), andgenerally the second stage coal liquids contain less hydrogen and moreasphaltenes than the product of the first liquefaction step. It may thusbe desirable to hydrogen treat the coal liquids recovered in the presentprocess from the second extraction step. The monocyclic aromatic solventused in the second extraction step may be conveniently flash distilledoff to separate it from the heavier coal liquids recovered in the secondextraction step, and the aromatic solvent can then be further utilizedin subsequent operation of the second stage extraction step.

The following examples are presented to illustrate the operation of theprocess of the present invention and to indicate some preferred modes ofcarrying out the present process. The examples are intended solely asillustrations and are not considered to indicate limitations on thegenerally broad scope of the present process as hereinbefore described.

EXAMPLE I In this run, a hydrogenated vacuum bottoms fraction from anAmerican petroleum source was used as the liquefaction solvent in thefirst stage liquefaction step and benzene was employed as the monocyclicaromatic hydrocarbon solvent in the second stage extraction step. Theliquefaction solvent had been prepared by processing petroleum vacuumbottoms at 760F. and 200 atmospheres hydrogen pressure in a continuoushydrogenation operation using a conventional catalyst at a liquid hourspace velocity (defined as volume of hydrocarbons processed per hour pervolume of catalyst) of about 0.5. The hydrocarbons resulting form thistreatment were fractionated and the bottoms product boiling above 850F.was recovered as the liquefaction solvent for use in this run. Analysisof this solvent indicated it contained 50 weight percent hydroaromatics,40 weight percent saturated aliphatics, and 10 weight percent condensedring aromatics. It had an API gravity of 20.0 and contained 1 weightpercent heptane insoluble components. In the first liquefaction step inthis run, a 200 gram sample of this liquefaction solvent and 200 gramsof an Illinois Belleville District Coal, pulverized to mesh and finerparticles, were placed in an 1,800 cc. rocking autoclave. The hydrogencontent of the original coal in this run was found to be 5.2 weightpercent The autoclave was sealed and sufficienthydrogen was introducedto provide 100 atmospheres hydrogen pressure. The contents of theautoclave were heated to 750F. and agitated at that temperature for 4hours. The autoclave was then cooled and excess pressure was released.The mixture of solids and liquids remaining in the autoclave was removedand the solids were separated form the liquids by centrifuging themixture. The liquids were recovered as the product of the liquefactionstep and analyzed. It was found that 47.0 weight percent of the originalcoal had been con verted to distillable liquid products in the firstliquefaction step. The first stage product had an API gravity of 20.1and contained only 1.1 weight percent heptane insoluble components. Thefirst stage product was thus found to be readily distillable andsubstantially free from asphaltenes. The solids recovered from the firstliquefaction step were analyzed and found to contain 5.2 weight percenthydrogen, indicating that the coal not converted to liquid products inthe first stage liquefaction step had not been degraded during the firstliquefaction operation. In the second stage extraction step, thepentane-insoluble solid residue from the first stage liquefaction wasplaced in a conventional Soxhlet extractor and extracted with benzene at175F. and at mospheric pressure. After 4 hours of extraction at theseconditions, which are notably mild extraction conditions for use inextraction of coal, the extraction operation was discontinued. The solidresidue resulting was separated from the benzene solvent and liquefiedsecond stage product. The product of the second stage extraction wasthen separated from the benzene solvent by flash distillation of thebenzene. It was found by analysis of the product that 35.5 weightpercent of the original coal had been recovered as benzene-solubleliquids in the second stage extraction operation. The combinedconversion of the original coal to hydrocarbonaceous products in thefirst and second stage extraction operation was thus 82.5 weightpercent.

EXAMPLE ll In this run, a hydrogenated vacuum bottom faction from amideastern petroleum source was used as the first stage liquefactionsolvent and benzene was used as the second stage monocyclic aromaticextraction solvent. The first stage liquefaction solvent in this runhave been derived by hydrogen treating petroleum vacuum bottoms at 750F.and 200 atmospheres hydrogen pressure using a conventional hydrogenationcatalyst at a 0.5 LHSV. The resulting hydrocarbons were hot flashed andthe bottoms product was employed as the liquefaction solvent in thisrun. This liquefaction solvent had an API gravity of l8.8, and anintitial boiling point of 475F. It contained 1.1 weight percentheptane-insoluble material. Analysis of this liquefaction solvent showedthat it contained 49 weight percent bydroaromatic hydrocarbons, 46weight percent saturated aliphatic hydrocarbons and 4 weight percentpolycyclic aromatics. A 200 gram sample of this liquefaction solvent and200 grams of the same coal, pulverized to 100 mesh particle size, usedin Example [were placed in the same 1,800 cc. rocking autoclave used inExample I. The autoclave was sealed and sufficient hydrogen was chargedto provide 100 atmospheres hydrogen pressure. The content of theautoclave were heated to 750F. and agitated for 4 hours at thattemperature. The autoclave was then cooled and excess pressure wasreleased. The mixture of liquids and solids in the autoclave was removedand the liquids were separated from the solids by centrifugation andrecovered as the first stage product. It was found that 58.1 weightpercent of the original coal had been converted to liquidhydrocarbonaceous products in the first stage liquefaction step. Theliquids recovered from the first stage lique-' faction step wereanalyzed and found to have an API gravity of about 205 and aheptane-insoluble content of only 1.2 weight percent. The solidsrecovered from the first liquefaction step were also analyzed and foundto contain 5.95 weight percent hydrogen as compared to only 5.2 weightpercent hydrogen in the original coal before the first stageliquefaction operation. The first stage liquefaction operation thusincreased the hydrogen content of the undissolved, solid coal recoveredafter the first stage operation. In the second stage solvent extractionstep in this run, the pentane-insoluble solids recovered from the firstliquefaction step were placed in the Soxhlet extractor used in Example Iand extracted with benzene at a temperature of 175F. and atmosphericpressure. After a period of 6 hours, the extraction operation wasdiscontinued and the benzene solvent and coal liquids were separatedfrom the remaining solid residue by filtration. After analysis of theliquids and solids recovered in the second stage, it was found that 18.6weight percent of the original coal had been recovered as benzenesolubleliquids in the sec- 0nd stage extraction operation. The two steps ofextraction in this run, according to the present invention, thusproduced a total conversion of solid coal to hydrocarbonaceous liquidproduct of 76.7 weight percent of the original coal.

From the foregoing description and examples, it is apparent that theprocess of the present invention, employing two stages of extractionwith two different solvents, provides a novel and superior method forrecovering hydrocarbonaceous liquid products from coal. The productsrecovered in the first liquefaction step in the present process, using aheavy hydrocarbonaceous solvent containing a mixture of hydroaromaticand saturated aliphatic hydrocarbons, provides a first stage productwhich is readily distillable and substantially free fromheptane-insoluble components. The second stage operation may beperformed at extremely mild operating conditions and enables almostcomplete conversion of carbonaceous materials on the original coal toliquid hydrocarbonaceous products with a desirably small investment inutilities and equipment because of the mild conditions employed.

We claim as our invention:

1. A process for the liquefaction of coal which comprises the steps of:

a. contacting the coal, at a temperature of from about 600F. to about850F., a pressure of at least about atmospheres and a time period offrom about /2 to about 24 hours, with a liquefaction solvent comprisinga partially hydrogenated condensed ring aromatic hydrocarbon boilingabove about 400F. and having from 1 to 4 adjacent CH groups in which thecarbon atom of the CH group forms part of the condensed ring structure,said solvent further comprising an alkane or cycloalkane C and heavierhaving a boiling point above about 400F., the weight ratio of thefirst-mentioned solvent component to the second-mentioned solventcomponent being from about 1:2 to about 2:1; separating the resultantmixture into a solids phase and a liquids phase;

recovering a first hydrocarbonaceous product from said liquids phase;

contacting said solids phase with a benzene or alkylbenzene solvent, thealkylbenzene having an alkyl group of from 1 to 4 carbon atoms, at atemperature of from about 50F. to about 300F., a

4. The process of claim 1 wherein said partially condensed ring aromatichydrocarbon contains at least 3 benzene nuclei.

5. The process of claim 1 wherein the solvent employed in step (d) isbenzene.

6. The process of claim 1 wherein said secondmentioned solvent componentof said liquefaction solvent is a mixture of paraffmic and naphthenichydrocarbons.

1. A PROCESS FOR THE LIQUEFACTION OF COAL WHICH COMPRISES THE STEPS OF:A. CONTACTING THE COAL, AT A TEMPERATURE OF FROM ABOUT 600*F. TO ABOUT850*F., A PRESSURE OF AT LEAST ABOUT 100 ATMOSPHERES AND A TIME PERIODOF FROM ABOUT 1/2 TO ABOUT 24 HOURS, WITH A LIQUEFACTION SOLVENTCOMPRISING A PARTIALLY HYDROGENATED CONDENSED RING AROMATIC HYDROCARBONBOILING ABOVE ABOUT 400*F. AND HAVING FROM 1 TO 4 ADJACENT CH2 GROUPS INWHICH THE CARBON ATOM OF THE CH2 GROUP FORMS PART OF THE CONDENSED RINGSTRUCTURE, SAID SOLVENT FURTHER COMPRISING AN ALKANE OR CYCLAKANE C12AND HEAVIER HAVING A BOILING POINT ABOVE ABOUT 400*F., THE WEIGHT RATIOOF THE FIRST-MENTIONED SOLVENT COMPONENT TO THE SECOND-MENTIONED SOLVENTCOMPONENT BEING FROM ABOUT 1*2 TO ABOUT 2*1; B. SEPARATING THE RESULTANTMIXTURE INTO A SOLIDS PHASE AND A LIQUIDS PHASE; C. RECOVERING A FIRSTHYDROCARBONACEOUS PRODUCT FROM SAID LIQUIDS PHASE; D. CONTACTING SAIDSOLIDS PHASE WITH A BENZENE OR ALKYLBENZENE SOLENT, THE ALKYLBENZENEHAVING AN ALKYL GROUP OF FROM 1 TO 4 CARBON ATOMS, AT A TEMPERATURE OFFROM ABOUT 50*F. TO ABOUT 300*F., A PRESSURE OF FROM ABOUT 1 TO ABOUT 10ATMOSPHERES AND A TIME PERIOD OF FROM ABOUT 1/2 TO ABOUT 24 HOURS; ANDE. RECOVERING A SECOND HYDROCARBONACEOUS PRODUCT FROM THE MIXTURERESULTING FROM STEP (D).
 2. A process according to claim 1 wherein saidliquefaction solvent has an initial boiling point of greater than about500*F.
 3. A process according to claim 1 wherein said benzene oralkylbenzene solvent is selected from benzene, toluene, xylenes,ethylbenzenes and isoproylbenzenes.
 4. The process of claim 1 whereinsaid partially condensed ring aromatic hydrocarbon contains at least 3benzene nuclei.
 5. The process of claim 1 wherein the solvent employedin step (d) is benzene.
 6. The process of claim 1 wherein saidsecond-mentioned solvent component of said liquefaction solvent is amixture of paraffinic and naphthenic hydrocarbons.